Automatic index level control circuit



Sept. 22, 1959 B. D. LoUGHLlN AUTOMATIC INDEX LEVEL CONTROL CIRCUIT 2Sheets-Sheet 1 Filed Dec. 14, 1955 Sept. 22, 1959 B. D. LouGHLlN2,905,752

AUTOMATIC INDEX LEVEL CONTROL CIRCUIT Filed Dec. 14, 1955 2 Sheets-Sheet2 United States Patent 2,905,152 AU'roMAno mDE-X'Lnzvur coNfrnoLjCIRCUIT- Bernard'l). Loughlin, Lynhrook, NAJL, assigner toHazeltineResearch, Inc., Chicago, ,111., a `corporation of Illi- 11.015

Application'December 14, 1955, SerialNo. 553,139

A5 Claims. (Cl. 178,-5.4)

This invention relates to color-image-reprcducing apparatusforfcolortelevision receiversand, moreV particulady, t0 .apparatus 0fthe WP@ which employs a Cathaderay image reproducer. in which acathode-ray beam sequentially scansY colorl elements to reproduce acomposite image and inewhich there is developedan indexing signalrepresentative of scanning frequency and phase of .given color elementsby the cathode-ray beam. For convenience, such a cathode-ray imagereproducer will be referredto hereinafteras a reproducer ofthebeamindexing type. Y

A Some prior cathoderay image reproducers `of the beam-indexing typehave employed cathode-ray tubes having phosphor screens comprising red,green, and blue light-emissive phosphor stripes disposed in repetitivesuccessionnormal vto line scan. The color-repetition frequency of l.thepicture signal .applied :to the ,cathode-ray tube, that is,.thefrequency. .ofthe color elements, is -synchronircd with thecolorfelement scanningfrequency. Forexample, thered'color ,elements mayvbe scanned at a.7n1ega'cycle rate, more or less; The same is true ,ofthe blue and green elements. Accordingly, the red, green, and bluecolorrepeti-tion frequency of the picture signal applied to thereproducer.- should be 7 megacycles infsynchro'nism with the scanning ofcorresponding color elements.`

Dueto nonuniformityofcolor element scanning caused, for example, bynonuniform distribution of phosphor stripes on thecathode-.ray,tubescreenor by nonlinearities of the line scan, the lcolor-element .scanning frequency and phase var yfacrossthe image raster.Accordingly, in prior vreproducersTof the beam-,indexing type,anindexing signal has been d eveloped'at a suitable indexing electrodeto ,synchronize the ,frequency and "phase of the picture signal -appliedto the cathode-rayV tube with vthe color element scanning frequency.

Heretofore, rcproducers o f lthe beamindexingtype have, `in general,employed secondaryremissive strips for developing aninlc'xing signal;However, some secondary .emissioni from surfaces lbetween the indexingstrips also occurred.l The secondary-emission ,currents from theindexing strips and ,the `surfaces between the indexingstrips-Variedfinaccordance with the color signal applied :i0 .thecathode-ray bearnv-.intensity control circuit of the cathoderay tube.Moreovenin 'order to provide a wide contrast range, alowminimum level ofindexing signal .was required for reliable'voperation. Hence, thesecondary-,emission effects, VYdue to the color signal, Vcausedappreciable color-signal interference with the indexing signal.Accordingly, ito* minimize color-signal interference withv the indexingsignal, it has been the practice toderive .the indexing signal from theAcathode-ray tube as a side-frequency modulation component of a carriersignal introducedlinto the systenrand-v-having-afrequency of, forexample, 52 megacycles.

`Moreover, because color signals have previously Vbeen applied totlre,c-:athoderay beam-'intensity control circuits and because of nnonliriearities'of the electron gun nbleam` 2,905,752 Patented Sept. 22,1959 ICC the indexing-Signal Carrier between harmonic CQmPQnatS' oftheharmonic components. Thus, it has heretofore b of'thec olor signal. Asthe frequency of the indexing signal varied, the Vcorrespondingside-frequency cornponent of theA carrier signal varied accordingly andVthe frequency of thecolor signal was caused -to `vary inr-lilce manner.However, the frequency variation of the'generated harmonic components ofthe color signal was much greater vthan the variation of thekside-,frequency` component representing the indexing lsignal because thefrequency'multiplication involved inthe generationA eenv necessaryV torestrict then frequency :variationof:A theindexing signal to a valuesuiiciently small that inter-y ferencebetween the harmonic componentsyof `the color signal and the side-frequency componentV representing theindexing signal was tolerable. This requirementedid not:allow' widetolerances inthe distributionofithe phosphorfstripes of the cathode-raytube screen'orv in the linearity line scan. i A' l y i In accordancewith the invention described and claimed in the copending application ofD. Loughlin andAl. V. Loughren, entitled Color-Image-Reproducing-Apparatus, Serial No. 552,443, ledDecember l2,A lf955, interference withthe indexingsignal ordinarily caused 'by harmonics ,of the color signalcan be substantiallyelimi-V nated by imposing the color signal on Ytheapparatus as a velocity-modulation component ofthe'line scan. Further,interference with the indexing signal Vcausedffzby the fundamental colorsignal maybe reduced toa suciently small value that the indexing signalmay be derived at vthe fundamental frequency rather than ,as aside-,band component of a carrier signal, thereby eliminating'fthe needfor a carrierl generator and associated'circuitsi i When employingvelocity modulation of line scan kt0 apply .the color signal or othercomponents of fthe vido signal to the image-reproducing apparatus,the'indxing-A signal amplitude may yfall below a` desired minimunilevielbecause the velocity modulation overV certain reg-ions of the tube facewill 'increase the scanning velocity/of the cathode-ray'beam as itsweeps over the indexing strip' and thus will decrease the totalsecondary emission yof the indexing strip; Additionally, the velocitymodulation may cause the raster developed by the indexing-,signalcathoderay beam of apparatus having an indexingfsign'al gunanda'picture-signal gun' to assume varying colors. Such a raster ofvarying colors is more noticeable vthan the `substantially white rasterwhich `would'be vdeveloped if the minimum indexing-signal amplituderemainedconstant, that is, if the indexing-signal amplitude "due to the`indexing-signal beam remained constant. lt is' ani'object of the presentinvention, therefore, ,to provide a new and improvedcolor-image-reproducing apparatus for a color-,television receiver whichavoidsone or more disadvantages of prior such apparatus.

lt yis another object'ofpthe invention to provide a new andy vimprovedcolor-imagefrep'roducing apparatus 'employinga cathode-ray imagereproducer of thebfearnindexing type and employing velocity-iriodulation."for y applying the color signals 'to the reproducer inwhich the indexing signal lils .maintained above a given yminimumamplitude level.

Itis another object of the invention to provide` a new and improvedcolor-image-reproducing apparatus employing' cathode-'ray imagereproducer ofthe' 'beamindexing type having an indexing-signalcathode-ray and a picturesignal beam and `employing ,velocity nio uflation for applying the color signals to the reproducer in which theindexing-signal cathode-ray beam develops a substantially white raster.

In accordance with a particular form of the invention,color-image-reproducing apparatus for a color-television receivercomprises circuit means for supplying a picture signal representative ofa color image to be reproduced and cathode-ray image-reproducing meanshaving a display screen comprising color elements and including indexingmeans for developing an indexing signal representative of the scanningof the color elements by the cathode-ray beam. The apparatus alsoincludes circuit means coupled to the cathode-ray image-reproducingmeansfor effecting scanning of the color elements by the cathode-raybeam and responsive to the indexing signal for controlling the relationof the scanning of the color elements and the color repetition of thepicture signal and responsive to the picture signal for varying thescanning velocity in accordance with the image to be reproduced todevelop a color image. lThe apparatus also includes circuit meansresponsive to the picture signal for modulating an indexing signalcomponent of the cathode-ray beam inversely of the scanning velocityvariations to maintain the indexing signal above a given minimumamplitude level.

For a better understanding of the present invention, together with otherand further objects thereof, reference is had to the followingdescription taken in connection with the accompanying drawing, and itsscope will be pointed out in the appended claims.

Referring to the drawing:

Fig. l is a circuit diagram, partly schematic, of a colortelevisionreceiver including color-image-reproducing apparatus constructed inaccordance with the invention;

Fig. 2 is a graph to aid in explaining the operation of the Fig. 1embodiment, and

Fig. 3 is a circuit diagram of an inverse modulator utilized in the Fig.1 apparatus.

Referring now to Fig. 1 of the drawing, the receiver includes an antennasystem 11, 11 of conventional construction to which the following areconnected in cascade: radio-frequency stages and detector 12, also ofconventional construction, for deriving video-frequency modulationcomponents of the received television signal with chrominance componentsat approximately 3.6 megacycles; a code translator 13, of conventionalconstruction, preferably of the type described in an article by B. D.Loughlin, entitled Processing of the NTSC Color Signal for One-GunSequential Color Displays, Proceedings of the I.R.E., January 1954 andalso known as a Y-to-M converter and subcarrier modifier for convertingthe video-frequency modulation components to a so-called dot-sequentialsignal having chrominance components at approximately 3.6 megacycles anda luminance-correction component; and a video-frequency amplilier 14having a pass band of, for example, -3 megacycles for translating thecorrected luminance signal to the display apparatus. The video-frequencyamplifier 14 constitutes first circuit means for supplying a signalprimarily representative of the luminance of a composite color image tobe reproduced.

There is also provided second circuit means for supplying a signalprimarily representative of the color of the image to be reproducedcomprising a band-pass filter 15 having `a pass band of, for example,3.0-4.2 megacycles for translating the corrected chrominance componentsand the color burst signal.

The receiver also includes a suitable synchronizingsignal separator 13for separating the line-scan and lieldscan synchronizing components fromthe output signal of the detector of unit 12. The separator 18 appliesthe linescan and field-scan synchronizing components to line-scan andfield-scan generators 19 and 20, respectively, included in the scanning-circuit means of the color-image-reproducing apparatus' for developingan image raster.

The receiver also includes a conventional sound-reproducing system 21coupled to the unit 12 for reproducing sound in the usual manner.

The color-image-reproducing apparatus includes cathode-rayimage-reproducing means having cathode-ray beam-intensity control meanscoupled to the first supply circuit means and havinga display screencomprising color elements and including indexing means for developing anindexing signal representative of the scanning of the color elements bythe cathode-ray beam. More particularly, the cathode-rayimage-reproducing means comprises a cathode-ray tube 22 of thebeam-indexing type and of conventional construction. The tube preferablyhas two electron guns of which only the common cathode and rst controlelectrodes are represented in the drawing. The tube also has an anode 23connected to a suitable source of positive potential -l-B and an outputelectrode 24 for collecting the secondary electrons representing theindexing information and connected to a source -l-B1. There areassociated with the tube, line-scan windings 25, 25 and field-scanwindings 26, 26 connected to the line-scan and field-scan generators 19and 20, respectively, for effecting scanning'of the color elements bythe cathoderay beam. Auxiliary line-scan windings 27, 27 are suppliedfor a purpose explained subsequently.

For clarity of expression, the term indexing signal will be employed torefer to a signal which carries information representing the scanning ofthe color elements of the display screen although this signal mayundergo frequency conversion and also carry additional informationduring translation.

The apparatus also includes circuit means responsive to the picturesignal and, more particularly, to the color signal for modulating thecathode-ray beam inversely of the scanning velocity variations tomaintain the indexing signal above a given minimum amplitude level andto maintain a substantially White raster due to the indexingsignalcathode-ray beam. This circuit means comprises auxiliary line-scanwindings 27, 27 and associated connections to a buffer 50 which is, inturn, connected to the indexing-signal gun of the cathode-ray tube 22.The windings 27, 27 and the buffer 50 are coupled to the buffer 33 andare responsive to at least the fundamental component of the picturesignal and are effective to derive a signal inversely representative ofthe scanning velocity variations for varying the bias of theindexingsignal gun inversely of the scanning velocity variations. Thewindings 27, 27 derive a voltage signal representative of the derivativeof the current therethrough, the current being the picture signaleffective to cause displacements of the cathode-ray beam. It is wellknown that a derivative signal may be derived from an original signal byintroducing a leading phase shift of and modifying the amplitude inproportion to frequency.

There is also provided signal-generating circuit means including anoscillator 34 for supplying an indexing- Signal carrier for modulatingthe indexing-signal cathoderay beam at a frequency of, for example, 52megacycles to provide a low-level indexing-signal carrier.

The color-image-reproducing apparatus preferably also includes circuitmeans for supplying a subcarrier reference signal synchronized with thecolor burst of a received composite video signal. This circuit meanscomprises a reference-signal generator 28 coupled to the band-passfilter 15.

The scanning circuit means of the apparatus includes, in addition to thegenerators 19 and 20 and the windings 2S, 25, 26, 26, and 27, 27, meansresponsive to the indexing signal for controlling the relation of thescanning of the color elements and the color repetition of the colorsignal and responsive to the color signal for varying the scanning inaccordance with the color of the image to beY reproduced to develop acomposite color image. This means preferably includes an`indexing-signal amplijier 2Q :responsive to indexing signal Yforapplying the same to a modulator 530 also responsive to the subcarrier"reference lsignal for deuivingaheterodynesignalrepresentative:of-theindexing signal. A modulator 31 alsoincluded-in the-last-'mentionedmeanslhas one input'circuit coupled tothemodulator 30land another input circuit coupled=through an inverse'-modulator 32 to the band-pass lter 15 for deriving a color signalhaving'its color-repetition frequency synchronizedwith YtheV colorelement scanning frequency.

The inverse-modulator 32*hasY a second input circuit coupled to theoutput circuito f the video-frequency amplifier 14 for deriving from thecorrected chrominance and 4luminance signalsapplied theretorbytheband-passlter 15 -andi theamplifier'14, 1'espec-:tively,` a signal rep--resentative-of the -chromaticity ofthe. image to -be -re produced. Thechromaticity of the image to be' reproducedfisV independent of the"luminance. The inverse modulator 32 "may beof"conventional'construction, for

example, ofY the type describedin- Patent No. 2,851,517A

apparatus-preferably also includes circuit means respon-l sive to theindexing signal and the color signal derived by the-modulator 31 forderiving asecond colorsignal having a frequency at thesecond harmonic ofthe colorA signal derived 'bythe-modulatorsl- This circuit meansincludes the'modulator 30,- whieh responds-to the output signal of theindexing-signal amplifier 29 and to the output signal of:.oscilla'tor34, for deriving-.a heterodyne signal representing the indexing signal.circuit 'of' the modulator-translatingthis -heterodyne signalis cou-pledthrough a frequency multiplier 35" having a-multiplication factorof forexample 3, to amodulator- 3.6' having another input circuit ycoupled tothe modulator 31.Y The-output signal of the modulator: 36 is -atVthe:second--liarmonic of f-the color-signal derived lby the modulator31,'andfthe modulator 3.6-is-coupled to the windings 27', 27fto vary thescanning. velocity in `accordance with the derived second harmonicsignal.

Referrring now `to Eig.- 3, the inverse-modulator 32. is thereyrepresented` in detail.' Ank input terminali 64I`is coupled through aphase. inverter 66Yand a condenser 67` to a control electrode,specifically the outer signalV input grid which 'is Loff-theremotecutoff `type-of` a mixer Vacuum tube 68:v A clamping diode 69lhas itsanode` eff), cur-,ve .of the. .remote cuto grid' :resembles Jthe curveof anegativeinverse function.. That is, 'the rfeg-ipy lcurve over agiven portion closely approximates a hyperb'ola` of the typerepresenting a functionk having one coordinate varying as the negative.reciprocal ofthe. other; Therefore, if a signal is applied to the remotecutoff grid, there will bev developed in the. anode current fa negativeinverse of the applied signal. Since a 'conventional modulator normallyproduces an output current flow proportional to the product of theapplied signals, if a negative signal is applied to the remote cutoffgrid by the phase inverter 66, the operation of the tube 68 is such thatthe resultant current ow throughtheload reproducing apparatus',Y the.cathode-ray beam l (includingV th`e' Vindexing-signal*beam.)`v ofthetube 2K2v during veach linescanlsequentiallyfscans thecolor elementsor'stripes offtlie'fcathode-ray tube and develops at' the indexingelectrode-241m'- indexing signal representative ofthe scanningof-s'tripes of-'a given color Due tov nonuniforrn'- ity-ofcolorelementiscanning caused, forY example, by no nuniform distributionofphosphork stripes-- on the cathodefray tube"l screenfor byAnon-"linearities` of'- line scan, thecolorfelementscanningfrequencyandiphase vary across-'the image raster?. This scanningfrequency may, for example-,t be approximately' 7'megacyclesv forsystems operating with UitedStates standards'and, ordinarily, variesacross each line as the line iSsGannedWith, atmost, a -slightvariationfat'ield-scan frequency. y

Because ofoseillator34;which`supplies a carrier signal-for'the indexingsignal, the indexingsignal developed atJthe'output electrode` 2`4lofthetube 22fmay have a varyinglfrequency of, for example, approximatelymegacyclescorresponding -toa `side frequency of the carrier signal.This-indexing `signal isfarnplified-by the amplier- 2.9fand applied to*modulator 301wherein it beats withV the output signal 'of Vthe:oscillator 34having a frequency of., for example, 52?megacyclesand-With. the'reference signal froml unit-28 thavinga.frequency of approximately 356 megac-ycles` to develop a heterodynesignal-having a frequency of, fon-example, 10.6 megacycles.

The heterodyne outputlsignal of the modulator 30v is applied 1to1thefmodulator l 31' While the picture signals and, in particular, thecorrected color components translatedibytheY/band-pass lter 15 areapplied to another input circuit of the` modulator 311V afterconversionto cli-romaticityl Acomponents inthe inverse'modulator 32 in response to:the -application lofthe corrected luminanceA signal` to the :modulatorv32 lbytheamplifier 14.i Thesig# nals. appliedftoV the modulator 31`beat togetherv in the modulatorltoldeyelop output color signals having afre-l quency off-approximately-7 megacycles for application tothefauxiliarywindings .27, 27"via the Vbuffer amplifier 33;

The -phasesand amplitudevofV the color signals applied to-thewindings-27, 27fare leffective to control the colors reproducedbythetube .225 bycontrolling the velocity of thercathode-ray` beam as itscans .the individual stripes of. the vcatliode-.rayA-tube. As thevelocity of scanning a given-f.set iofstpes, for example, the redstripes, istincreased;V lessred iszapparent inthereproduced image.Likewise,v as=the velocity of'lscanningthe red Vstripes isdecreased,moreredfis apparent in -thereproduced image; Inzzthismanner,.thes'canningzvelocity varies in` accordancewith vthe 'appliedacolorsignal .to reproduce Ythe compositeiimage.

The variation `ofscanning: velocity with the appliedcolorz'signalisrepresentedwin 1"ig...2A whichcis a graph representingthe time-space characteristic of a line scan. Gul-.ve Y,Are'presents a-horizontalfline scan withno i appliedi color signal: and. thus no.`.velocity modulation. Curve Bzrepesents aline scan withvelocitymodulation which increasesthered-light output andfdecreases thegreenalight'and zblueslightroutpnts'by increasingv the vbeamdvvel'lftim'e onthev red'.y stripes and decreasing the beamdwellttimeon'zthe'green and 'blue stripes.'

It-'will :be 1understood lthatitlie static phase may be:controlledfduringinitialadjustment by, for'example, adjustmenttofVthepliase of'the. output ysignal of the; generatorf28- .lvl/bile. theamplitude mayl be controlled conveniently by-'anyfconventionall gainadjustment of the color-signal-translating channel.

Whilewthe application of the `fundamental component 0f: vthecolor-signal tothe. cathode-ray tube 22 reproduces' acolorjimagefmaccordance With/the applied color signalg theA color signal l-atthefundamental frequency rof 7 7 megacycles represents only anapproximation of the ideal scanning signal which would reproduce thepicture perfectly. For example, highly saturated colors will not beperfectly reproduced. The picturequality may, therefore, be improved bysupplying one or more additional harmonics of the color signal in properphase and amplitude so that the ideal scanning signal is more closelyapproximated. Accordingly, a second harmonic of the color signal issupplied in the following manner.

kThe modulator 30 has one output circuit tuned to 7 megacycles to derivean indexing signal at 7 megacycles with frequency variations in responseto the output signals of the amplifier 29 and the oscillator -34. This7V-megacycle signal is supplied to the multiplier 35 wherein it ismultiplied by a factor of 3 to provide a ZI-megacycle signal forapplication to the modulator 36. The output signal of the modulator 31,representing the color signal at 7 megacycles, is applied to anotherinput circuit Aof the modulator 36 to derive a color signal at 14megacycles with `frequency variations of the indexing signal in theoutput circuit of the modulator 36 for application to the windings 27,27 to control the scanning velocity in conjunction with the outputsignal of the buier 33. The phase and amplitude of the l4-megacyclecolor signal relative to the 7-megacycle signal applied to the windings27, 27 may be suitably controlled by phase and gain adjustments of units35 and 36.

Considering now the conjoint operation of the oscillator 34, the buffer50, and the auxiliary line-scan windings 27, 27, the oscillator 34applies its output signal to the cathode-ray tube 22 where the scanningvelocity variations Would cause the derived indexing-signal amplitude tofall below a given minimum level over regions of the cathode-ray tubeface in the absence of correction. That is, the component of theindexing signal derived at electrode 24 due to the indexing-signalcathode-ray beam would not remain constant. This component determinesthe minimum amplitude of the indexing signal which exists when thepicture-signal beam iscut off during black portions of the picture. .v

In accordance with the invention, to maintain the indexing signal abovea given minimum amplitude level, the auxiliary line-scan windings 27, 27develop a voltage signal from the current signal from modulator 36 andbuier 33 which is the derivative of the current signal. The currentsignal is representative of displacement variations of the cathode-raybeam. Thus, since the voltage signal derived by the windings 27, 27represents the derivative of the current signal, the voltage signalr isrepresentative of the scanning velocity variations. `Accordingly, thebuffer 50 varies the bias of the indexingsignal gun inversely of thescanning velocity variations to increase the intensity of theindexing-signal cathoderay beam during intervals when the beam is movingrapidly over the indexing strips and to decrease its intensity when thebeam is moving slowly over the indexing strips. 4 v v In the mannerdescribed above, the indexing-signal amplitude is maintained above apredetermined minimum level because the component of the indexing signalat electrode 24 due to the indexing-signal cathode-ray beam ismaintained substantially constant.` Additionally, a substantially whiteraster is developed due to the indexing-signal beam because theintensity variations of the indexing-signal beam compensate for thevelocity variations as the beam sweeps across the phosphor stripes.

Because the color signal does not modulate the intensity of thecathode-ray beam, color-signal interference at fundamental frequency isminimized. Thus, for some applications it may be desirable to eliminatethe oscillator 34 and derive the indexing signal at a fundamentalfrequency of 7 megacycles. This will require modifying the translationfrequency of amplifier 29 to 7 mega- 8 cuit of amplifier 29 in lien ofconnection between units 35 and 30. To maintain the indexing-signalamplitude above a given minimum level, the windings 27, 27 may then becoupled to the indexing gun of the tube 22 through a suitable network inlieu of buffer 50.

Moreover, it will be apparent that while the Fig. l

system provides synchronization between the color ele` ment scanningfrequency and the color-repetition frequency of the applied picturesignals by controlling the color-repetition frequency of the picturesignals, the

invention is also applicable to systems which provideV synchronizationby controlling the color element scanning frequency by, for example,controlling the instantaneous sweep slope of the output signal of theline-scan generator.

While there has been described what is at present considered to be thepreferred embodiment of this invention, it will be obvious to thoseskilled in the art that j various changes and modifications may be madetherein without departing from the invention, and it is, therefore,aimed to cover all such changes and modiiications as fall within thetrue spirit and scope of the invention.

What is claimed is:

l. Color-image-reproducing apparatus for a colortelevision receivercomprising: circuit means for supplying a picture signal representativeof a color image to be reproduced; cathode-ray image-reproducing meanshaving a display screen comprising color elements and including indexingmeans for developing an indexing signal representative of the scanningof said color elements by the cathode-ray beam; circuit means coupled tosaid cathode-ray image-reproducing means for effecting scanning of saidcolor elements by said cathode-ray beam and responsive to said indexingsignal for controlling the relation of the scanning of said colorelements and the color repetition of said picture signal and responsiveto said picture signal for varying the scanning velocity in accordancewith the image to be reproduced to develop a color image; and circuitmeans responsive to said picture signal for modulating an indexingsignal component ofv said cathode-ray beam inversely of the scanningvelocity variations to maintain said indexing signal above a givenminimum amplitude level.

2. Color-image-reproducing apparatus for a colortelevision receivercomprising: circuit means for supplying a color signal representative ofthe color of a color image to be reproduced; cathode-rayimage-reproducing means having a display screen comprising colorelements and including indexing means for developing an indexing signalrepresentative of the scanning of said color elements by the cathode-raybeam; circuit means coupled to said cathode-ray image-reproducing meansfor eifecting scanning of said color elements by said cathode-ray beamand responsive to said indexing signal for controlling the relation ofthe scanning of said color elements and the color repetition of saidcolor signal and responsive to said color signal for varying thescanning velocity in accordance with the color of the image to bereproduced to develop a color image; and circuit means responsive tosaid color signal for modulating an indexing signal component of saidcathode-ray beam inversely of the scanning velocity variations tomaintain said indexing signal above a given minimum amplitude level.

3. Color-image-reproducing apparatus for a color-television receivercomprising: circuit means for supplying a signal representative of theluminance of a color image to .be reproduced; circuit means forsupplying a color signalrepresentative of the color of a color image tobe cycles and the provision of suitable connection between the inputcircuit of multiplier 3S and the output cirreproducing means forelecting scanning of said color elements by said cathode-ray beam andresponsive to said indexing signal for controlling the relation of thescanning of said color elements and the color repetition of said colorsignal and responsive to said color signal for varying the scanningvelocity in accordance with the color of the image to be reproduced todevelop a color image; and circuit means coupled to said supply circuitmeans for applying to said image-reproducing means a signal derived fromsaid color signal and having a phase and amplitude representative of thescanning velocity variations for modulating the intensity of an indexingsignal component of said cathode-ray beam inversely of said scanningvelocity variations to maintain said indexing signal above a givenamplitude level.

4. Color-image-reproducing apparatus for a color-television receivercomprising: circuit means for supplying a signal representative of theluminance of a color image to be reproduced; circuit means for supplyinga color signal representative of the color of a color image to bereproduced; cathode-ray image-reproducing means having an electron gunresponsive to said luminance signal for developing a picture-signalcathode-ray beam intensitymodulated by said luminance signal and anelectron gun for developing an indexing-signal cathode-ray beam andhaving a display screen comprising color elements and including indexingmeans for developing an indexing signal representative of the scanningof said color elements by the cathode-ray beams; circuit means coupledto said cathode-ray image-reproducing means for effecting scanning ofsaid color elements by said cathode-ray beams and responsive to saidindexing signal for controlling the relation of the scanning of saidcolor elements and the color repetition of said color signal andresponsive to said color signal for varying the scanning velocity inaccordance with the color of the image to be reproduced to develop acolor image; and circuit means responsive to said color signal forderiving a signal representative of the derivative of the color signalwhich causes displacements of said cathode-ray beams for modulating saidindexing-signal cathode-ray beam inversely of the scanning velocityvariations to maintain said indexing signal above a given minimumamplitude level and to maintain a substantially White raster due to saidindexingsignal cathode-ray beam.

5. Color-image-reproducing apparatus for a color-television receivercomprising: circuit means for supplying a picture signal representativeof a color image to be reproduced; cathode-ray image-reproducing meanshaving a display screen comprising color elements and including indexingmeans for developing an indexing signal representative of the scanningof said color elements by the cathode-ray beam; circuit means coupled tosaid cathode-ray image-reproducing means for eiecting scanning of saidcolor elements by said cathode-ray beam and responsive to said indexingsignal for controlling the relation of the scanning of said colorelements and the color Irepetition of said picture signal and responsiveto said picture signal for varying the scanning velocity in accordancewith the image to be reproduced to develop a color image;signal-generating circuit means coupled to said cathode-rayimage-reproducing means for supplying an indexing-signal carrier formodulating said cathoderay beam; and circuit means coupled to saidsupply circuit means and responsive to at least the fundamentalcomponent of said picture signal for deriving a signal inverselyrepresentative of the scanning velocity variations and coupled to thecathode-ray image-reproducing means for modulating an indexing signalcomponent of said cathoderay beam inversely of the scanning velocityvariations to maintain said indexing signal above a given minimumamplitude level.

References Cited in the tile of this patent UNITED STATES PATENTS2,227,630 Carnahan Jan. 7, 1941 2,671,129 Moore Mar. 2, 1954 2,723,306Creamer Nov. 8, 1955

